What is this?

Hi! Those little pests are tiny soil mites, they aren't dangerous by themselves, you have so many because your soil is too moist, they become dangerous if there's root rot, because they start eating the dead roots, which can worsen the infection :) To get rid of them, just let the soil dry out a bit (2-3cm) and then water with a specific product, preferably organic (neem or nettle/chili macerate). Happy growing!

There's a great app that might help identify this little guy... called iNaturalist... it's free and identifies pretty much anything in nature... I've used it to identify insects, plants, trees, birds... If you know what you are dealing with, you'll be able to figure out what, if anything, you need to do! Good luck!

Not good whatever they are .......but usually a sign that your soil mix is constantly too wet. 8 legs would indicate a mite of some sort.

It looks like there is white powder under the pot.

They may just be soil mites then, which I believe only eat decaying matter and would keep your soil healthy and leave your plant alone. I'd give a quick google and compare some pictures to what you're seeing and keep a close eye on the plants leaves moving forward for any damage / bugs.

They are on the soil, not on the leaves. They are white and red.

Hard to tell from the pics, but if they tiny enough that you need a magnifying glass to see them, have 8 legs and are pale white / brown they may well be spider mites. Are they also under any leaves? Are the leaves showing any speckling? If they are spider mites, theres a number of natural treatments to kill them off, but you'll have to be pretty dilligent in its application and depending on where you are with the grow would need to be careful about spraying anything directly onto buds.